Because it is artsy-fartsy and "deep" and "emotional" and "not entertaining" - this is a potent combination that completely overwhelms the senses of professional movie reviewers.
If it was for free I would love to play it, they look cool and relaxing, but I have never though of those games, well... as games... is only exploration of nice enviroments, like flower and journey; they don't fit in my definition of game.